Signal clipping protection using pre-existing audio gain metadata

Abstract

The application describes a method and an apparatus to prevent clipping of an audio signal when protection against signal clipping by received audio metadata is not guaranteed. The method may be used to prevent clipping for the case of downmixing a multichannel signal to a stereo audio signal. According to the method, it is determined whether first gain values (4) based on received audio metadata are sufficient for protection against clipping of the audio signal. The audio metadata is embedded in a first audio stream (1). In case a first gain value (4) is not sufficient for protection, the respective first gain value (4) is replaced with a gain value sufficient for protection against clipping of the audio signal. Preferably, in case no metadata related to dynamic range control is present in the first audio stream (1), the method may add gain values sufficient for protection against signal clipping.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001]This application claims priority to U.S. Patent Provisional Application No. 61 / 109,433, filed 29 Oct. 2008, hereby incorporated by reference in its entirety.FIELD OF THE INVENTION [0002]The patent application relates to clipping protection of an audio signal using pre-existing audio metadata embedded in a digital audio steam. In particular, the application relates to clipping protection when downmixing a multichannel audio signal to fewer channels.BACKGROUND OF THE INVENTION[0003]It is a common concept to embed audio metadata into a digital audio stream, e.g. in digital broadcast environments. Such metadata is “data about data”, i.e. data about the digital audio in the stream. The metadata can provide information to an audio decoder about how to reproduce the audio. One type of metadata is dynamic range control information which represents a time-varying gain envelope. Such dynamic range control metadata can serve multiple purposes:[0004...

AI Technical Summary

Benefits of technology

[0041]Instead of simply inverting the determined maximum, a gain value may be computed by dividing a maximum signal value (which corresponds to 0 dBFS) by the determined maximum associated with a data segment. However, the computational costs are higher compared to a simple inversion.

Problems solved by technology

Such dynamic range control metadata can serve multiple purposes:(1) Control the dynamic range of reproduced audio: Digital transmission allows for a high dynamic range, but listening conditions do not always permit taking advantage of that.

Although high dynamic range is desirable in quiet living room conditions, it may not be appropriate for other conditions e.g. for a car radio because of the high background noise level.

The latter approach is not preferable as it makes it impossible for a receiver to reproduce the audio with full dynamic range.

Often, the metadata accomplishes both tasks, but this is not always the case, so in some cases the metadata may not include downmix clipping protection.

Moreover, the incoming audio stream may not include dynamic range control metadata at all, due to the fact that for some audio encoding formats the metadata is optional.

If the dynamic range control metadata is not included with the compressed audio stream or is included but does not include downmix clipping protection, undesirable clipping artifacts may be present in the decoded signal if a multi-channel signal is downmixed into to fewer channels.

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